The majority of women with breast cancer undergo breast-conserving surgery, but in >20% of the cases it is post-surgically determined that the margins are not tumor free and additional surgery is necessary. One potential solution is the use of optical image-guided surgery to improve intraoperative margin assessment. We recently found that the near-infrared fluorescent dye, indocyanine green (ICG), can be used to help differentiate breast tumor tissue from normal tissue in clinical investigations; however, a low specificity was found to lead to false-positives. We hypothesize that targeted nanoparticles capable of carrying large payloads of ICG could be used to confer additional specificity (and sensitivity) during surgery. A recent trend in more aggressive cancer therapies involves treating patients with photodynamic therapy (PDT) as anadjunct to surgery. Clinical studies have shown that this can improve overall survival. However, PDT is hampered by the poor specificity of photosensitizers and the limited depth penetration of the excitation light. We propose to utilize targeting ligands to overcome the poor selectivity of sensitizing agents and ultrasound, instead of light, to activate the sensitizing agents to improve tissue penetration, i.e. sonodynamic therapy (SDT). ICG will be used as the sensitizer, thus allowing a single agent to be used for both imaging and therapy. The goal of this proposal is to develop multifunctional, targeted nanoparticles that allow intraoperative image- guided surgery and SDT to be performed in a novel combination regimen for treating breast cancer. Multifunctional nanoparticles will be prepared with ICG and superparamagnetic iron oxide nanoparticles (SPIONs) in a single nanoformulation. The nanoparticles will be designed to target fibroblast activating protein (FAP) on the tumor stroma. We hypothesize that stromal cells will be a favorable target because they are located at the invasive front of the tumor, they are genetically stable, and they are required for expansion of tumor initiating cells. Superparamagnetic iron oxide nanoparticle (SPION)-enhanced MR imaging is expected to enable preoperative radiologic findings to be directly related to the visual presentation of pathology during surgery. ICG-enhanced intraoperative image-guided surgery will enable more complete resection, resulting in fewer residual cancer cells after surgery. SDT will enable the ablation of any residual disease. We believe that this innovative nanotechnology will profoundly improve the ability of physicians to completely eradicate local disease in breast cancer patients, resulting in fewer re-excisions and an improvement in survival. The specific aims of this proposal are (1) . Synthesize and characterize the physical-chemical properties of FAP-targeted ICG-coated SPION nanoclusters.; (2) . Characterize binding, uptake and cytotoxicity of ICG- coated SPION nanoclusters in vitro; and (3) Evaluate the pharmacokinetics, contrast enhancement, and ability of ICG-coated SPION nanoclusters to enhance intraoperative image-guided resection and SDT in a murine model of breast cancer.